Joining element and method for the production of such a joining element as well as an integrally bladed rotor

ABSTRACT

A joining element, for example, an adapter, for connecting a rotor blade to a rotor disc or a rotor ring, or a rotor blade per se of an aircraft engine is disclosed. The joining element has a base body and a joining surface, with the joining surface formed by a fusion weldable coating made of a compressed powder that is connected in a positive fit to a contour of the base body. A method for the production of such a joining element, as well as an integrally bladed rotor, is also disclosed.

This application claims the priority of German Patent Document No. 10 2010 045 331.5, filed Sep. 14, 2010, the disclosure of which is expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a joining element and a method for the production of such a joining element.

Various production methods are known for producing a BLISK or a BLING (blade-integrated disc or blade-integrated ring) for jet engines such as aircraft engines. In one method, for example, the BLISK is produced in one piece from a disc by shaping its outer contour using a chip removal process in order to form blade profiles. In another method, the rotor blades are produced separately from the disc and connected to the outer circumference of the rotor disc by linear friction welding.

In order to increase the durability of turbine blades and compressor blades, it is increasingly common to use blades with a monocrystalline structure because such blades have virtually no crystal boundaries or other structural defects. However, when connecting the monocrystalline rotor blades to a polycrystalline rotor disc by friction welding, it is important to note that, depending on the crystallographic orientation of the monocrystalline material structure, another load may be necessary in order to bring the monocrystalline material structure into a plasticizable condition. Applied to the friction welding method, this means that the welding method for the monocrystalline material changes as a function of the crystallographic orientation of the monocrystalline material relative to the oscillation and pressure direction. In the least favorable case, the load required for friction welding may be so high due to the crystallographic orientation of the monocrystalline material that the machine tool or tool head is damaged.

In order to solve this problem, WO 2007/144557 A1 proposes that a monocrystalline component be orientated for linear friction welding in such a way that a primary gliding plane of the monocrystal is oriented to a plane that contains the oscillation direction as well as the pressure direction and such that a primary gliding plane of the monocrystal extends within a certain angle range relative to the oscillation direction. Although this method does allow the direct welding of a rotor blade to a rotor disc, the method is limited to oblong geometries. In addition, this method does not solve general problems of linear friction welding such as a thin, extremely smooth, and sometimes brittle diffusion zone as well as rapid crack propagation.

Therefore, MTU's German patent DE 10 2008 039 113 B3 proposes that a polycrystalline adapter, which is initially connected to the rotor blade by rotational friction welding, be disposed between a monocrystalline rotor blade and a polycrystalline rotor disc. After the production of the blade-adapter arrangement, the adapter is connected to the rotor disc by a fusion welding method or the like.

However, the adapter is subjected to high temperatures and chemical damage, particularly in the connective region on the side of the blade, such that a monocrystalline material structure is preferred, at least on the side of the blade.

The object of the present invention is to create a joining element, in particular for welding to a fusion weldable body segment of an element to be welded, that eliminates the disadvantages discussed above and has a joining surface that is fusion weldable independently of its base material, a method for producing a joining element of this type, as well as an integrally bladed rotor of a jet engine, in particular of an aircraft engine.

A joining element according to the invention, in particular for welding with an element to be welded, comprises a base body and a joining surface. According to the invention, the joining surface is formed by a fusion weldable coating made of a compressed powder that is connected in a positive fit to a contour of the base body. The joining element is thus fusion weldable in the region of its joining surface independently of the material of its base body. Thus, the contour achieves a mechanical, intensive compression of the coating to the base body, such that the coating is connected to the base body in a resilient manner. In addition, the coating, which may be a few centimeters thick, achieves a gradual expansion of the diffusion zone and therefore a gradual, soft transition of the elastic and fracture mechanical properties. Moreover, the coating prevents the propagation of cracks into the joining surface or into the joining region, because such cracks are only able to propagate up to the contour of the base body.

The greater the area of the contour, the more fundamentally stable the compression of the coating to the base body. In one exemplary embodiment, therefore, it is preferred for the contour to extend over a large area of a surface of the base body.

The coating preferably has a thickness that corresponds to a height of the contour. This allows the contour to penetrate the coating over its entire cross section such that the coating is prevented from shearing off in the case of a transverse load.

A particularly intensive mechanical compression may be achieved by designing the contour as a fractal structure. In a preferred exemplary embodiment, the contour is designed as a Koch curve, for example, according to the second iteration.

In one exemplary embodiment, the joining element is designed as an adapter for connecting a monocrystalline rotor blade to a polycrystalline rotor disc, with the base body being composed of a monocrystalline material and the coating being composed of a polycrystalline material corresponding to the material of the rotor disc.

In another exemplary embodiment, the joining element is designed as a monocrystalline rotor blade for attachment to a polycrystalline rotor disc, with the base body forming the rotor blade and the coating being applied to the blade. This allows a direct, fusion welding-based connection of the rotor blade to the rotor disc, whereby a BLISK or BLING of this type is made particularly resilient.

In an embodiment of a method according to the invention for the production of a joining element, first a base body is provided. The base body is then provided with a contour. Then the base body is framed in the region of the contour for the purpose of forming a powder basin. Then the power basin is filled with a polycrystalline powder, which is poured into the powder basin until the contour is completely covered by the powder. The powder is subsequently compressed under pressure and temperature in order to form a coating that is connected to the contour in a positive fit. After compression, the base body or contour is removed from the mold and, if necessary, the joining element is finished. The method according to the invention allows the production of a joining element made of two different materials that together form a body section that is connectable to a connecting element, the materials being securely connected to one another by mechanical compression. The mechanical compression is of such intensity that the joining element is able to be connected to another element to be welded in the region of its base body and its coating by a welding and soldering method.

In a method that is simple from a manufacturing standpoint, the base body is a cast, forged, or sintered metal body into which the contour is mechanically placed by partially lowering a surface of the base body. This may occur, for example, by a chip removal process such as milling, grinding, boring, and the like.

In another exemplary embodiment, the contour is placed into a surface of the base body thermally, for example, by wire erosion and/or electrochemical machining (ECM or PECM).

In a preferred exemplary embodiment, a surface of the base body is not lowered by segments, but rather provided with elevations by segments. To this end, the base body is produced with an integral contour in a generative fashion or by a generative production method such as selective laser sintering. This allows the contour to have virtually any geometric shape desired, such that even highly complex fractal structures can be reproduced as contours. In addition, no additional strains or changes to the material are introduced into the base body in the course of forming the contour.

In a method, the powder is connected to the base body by hot isostatic pressing, whereby the coating receives isotropic properties and a particularly highly compacted and thus intensive compression of the coating onto the contour results.

An integrally bladed rotor according to the invention of a jet engine, in particular an aircraft engine, has a plurality of rotating blades that are each connected to the outer circumference of the rotor by a joining element according to the invention, with the base body being disposed on the side of the rotating blades and the coating being disposed on the side of the rotor. A rotor of this type is particularly highly resilient because of the excellent connection of the rotating blades to the rotor resulting from the joining element.

Other advantageous exemplary embodiments of the invention may be found in the disclosure.

A preferred exemplary embodiment of the invention shall be described in greater detail in the following with reference to the schematic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective depiction of a joining element according to the present invention;

FIG. 2 is a perspective depiction of a preferred contour of the joining element shown in FIG. 1; and

FIGS. 3, 4, and 5 illustrate method steps for the production of the joining element shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIG. 1, a joining element 2 according to the invention, for example, an adapter for connecting a monocrystalline rotor blade to a polycrystalline rotor disc or for forming an integrally bladed rotor of a jet engine such as an aircraft engine, has a cuboid shape and comprises a base body 4 and a coating 6 that is connected to the base body 4 primarily by a positive fit.

The base body 4 is composed of a monocrystalline metal material and serves to connect the adapter 2 to the rotor blade, for example, by a rotational welding method, in the region of an outer surface 8 facing away from the coating 6. It has an integral contour 10 with a fractal structure for the purpose of forming a positive fit with the coating 6.

According to FIG. 2, the contour 10 extends in the longitudinal direction x and the transverse direction y of a surface 12 of the base body 4 facing away from the outer surface 8. It is preferably a Koch curve according to a second iteration having a central triangular projection 14 that is laterally flanked by two triangular projections 16, 18. On its flanks, the central projection 14 has two triangular protrusions 20, 22, below which two undercuts are formed, to which no reference characters have been assigned. The lateral projections 16, 18 have a lower extension in the vertical direction z (height) of the base body 4 than the central projection 14, with the left-hand projection 16 (h1) according to the depiction in FIG. 2 having a smaller design than the right-hand projection 18 (h2).

The coating 6 is composed of a compressed powder 24 (see FIG. 4) made of a polycrystalline metal material and, according to FIG. 1, has a joining surface 26 facing away from the outer surface 8 and pointing in the direction of the surface 12 for the purpose of connecting the joining element 2 to the rotor disc. In order to achieve an optimal connection between the rotor disc and the adapter, the powder 24 is made of the same fusion weldable material as the rotor disc, for example, Inconel 718.

In a preferred method for the production of the adapter 2, according to FIG. 3, in a first step, the base body 4 is generatively produced from a monocrystalline material with an integral contour 10 that comprises a plurality of projections 14, 16, 18.

Then, in a second step, the base body 4 is surrounded in the region of its contour 10 by a frame 28 that defines a powder basin 30 for accommodating a polycrystalline powder 24. Then the powder 24 is poured into the powder basin 30, such that free spaces or remaining volumes 32 a, 32 b, 32 c, 32 d of the contour 10 are filled between the projections 14, 16, 18 and between the projections 16, 18 and the lateral frame 28. The powder basin 30 is filled with the powder 24 in such a way that the contour 10 or its highest projection 14 viewed in the vertical direction z is covered with the powder 24 such that, after a compression of the powder 24 and final finishing of the adapter 2, the joining surface 26 is disposed at a distance from the surface 12 that corresponds to the height of the highest projection 14, thus corresponding to the height h of the contour (see FIG. 5).

Then, in a third step according to FIG. 4, the powder basin 30 is closed or the base body 4 and the contour 10 are encapsulated along with the powder 24 and sealed around their full circumference.

Then, in a fourth step according to FIG. 5, the powder 24 is compressed under temperature and pressure in the course of a hot isostatic pressing process until the powder 24 forms a homogeneous and isotropic resilient coating 6 that is connected by an intensive mechanical compression to the contour 10 and/or the surface 12 forming the contour 10.

Finally, in a fifth step, the adapter 2 is unmolded and the adapter 2 is finished to its target dimensions. After finishing, the adapter 2 comprises a monocrystalline base body 4 having a polycrystalline coating 6 that defines a fusion weldable joining surface 26. The thickness d of the coating 6 corresponds to the height h of the contour 10. The adapter 2 can now be joined to a rotor blade, for example, by a rotation friction fusion welding method, and then be joined as a blade-adapter arrangement in the region of the joining surface 26 to a polycrystalline rotor disc by a fusion welding method.

Disclosed is a joining element, for example, an adapter, for connecting a rotor blade to a rotor disc or a rotor ring, or a rotor blade per se of an aircraft engine, having a base body and a joining surface, with the joining surface being formed by a fusion weldable coating made of a compressed powder that is connected in a positive fit to a contour of the base body, a method for the production of such a joining element, as well as an integrally bladed rotor.

LIST OF REFERENCE CHARACTERS

-   2 Joining element -   4 Base body -   6 Coating -   8 Outer surface -   10 Contour -   12 Surface -   14 Central projection -   16 Lateral projection -   18 Lateral projection -   20 Protrusion -   22 Protrusion -   24 Powder -   26 Joining surface -   28 Frame -   30 Powder basin -   32 a, b, c, d Free space -   h Height -   h1 Height -   h2 Height -   d Thickness

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

1. A joining element, comprising: a base body, wherein the base body includes a contour; and a joining surface, wherein the joining surface is a fusion weldable coating of a compressed powder; wherein the joining surface is connected in a positive fit to the contour of the base body.
 2. The joining element according to claim 1, wherein the contour extends over a large area of the base body.
 3. The joining element according to claim 1, wherein the coating has a thickness that corresponds to a height of the contour.
 4. The joining element according to claim 1, wherein the contour has a fractal structure.
 5. The joining element according to claim 1 in combination with a rotor blade and a rotor disc, wherein the joining element is arranged between the rotor blade and the rotor disc.
 6. The joining element according to claim 1, wherein the joining element is a portion of a rotor blade of a jet engine.
 7. A method for production of a joining element, comprising the steps of: providing a base body; providing a contour to the base body; surrounding the base body with a frame, at least in a region of the contour, to form a powder basin; pouring a metal powder into the powder basin at least until the contour is covered by the metal powder; compressing the metal powder under pressure and temperature to form a coating that is connected to the contour in a form-fitting manner; and removing the frame from the base body.
 8. The method according to claim 7, wherein the step of providing the contour to the base body includes mechanically forming the contour.
 9. The method according to claim 7, wherein the step of providing the contour to the base body includes thermally and/or electrochemically forming the contour.
 10. The method according to claim 7, wherein the step of providing the contour to the base body includes producing the contour in a generative manner.
 11. The method according to claim 7, wherein the step of compressing is hot isostatic pressing.
 12. An integrally bladed rotor of a jet engine, comprising: a plurality of blades; and a rotor disc; wherein each of the plurality of blades are connected to an outer circumference of the rotor disc by a respective joining element according to claim 1 with the base body disposed on a side of the blade and the coating disposed on a side of the rotor disc. 